Compression rod actuator



March 4, 1969 R. E. SEAMANDS ET AL 3,430,541

COMPRESSION ROD ACTUATOR INVENTOR8 ROBERT E. SEAMANDS Filed March 28, 1967 BY JIMMY H. WILLIAMS .9 fi WW F- ATTORNEYS United States Patent O 3,430,541 COMPRESSION ROD ACTUATOR Robert E. Seamands, Moline, Ill., and Jimmy H. Williams, Bettendorf, Iowa, assignors to the United States of America as represented by the Secretary of the Army Filed Mar. 28, 1967, Ser. No. 627,252 US. Cl. 92-113 Claims Int. Cl. F0111 3/00 ABSTRACT OF THE DISCLOSURE The invention is concerned with a compression rod actuator wherein a hollow piston is pressure loaded in compression. A slip-fit, floating member is provided within the hollow piston to add to the column strength thereof without adding to the column load thereby to control excessive buckling stresses of the piston due to extreme axial loading.

BACKGROUND OF THE INVENTION The present invention relates to compression rod actuators and more particularly to an actuator employing means to improve the column strength of the assembly without adding to the column load.

Compression rod actuators are useful for a variety of functions and, therefore, for some applications, the actuator is made from relatively lightweight material even though high pressure is used as a motivating force. In some actuators the wall thickness of the piston is relatively thin and difficulties are encountered with buckling stresses caused by axial loading.

Accordingly, it is a primary object of the present invention to provide reinforcing means for a compression rod actuator which is effective in controlling excessive stresses of the piston as a result of extreme axial loading.

It is also an object of the present invention to provide an improved compression rod actuator which is adapted to a wide range of operating pressures and which will increase the column strength thereof without adding to the column load.

It is a further object of the present invention to provide a simple and efiicient means for reinforcing a hollow piston of a compression rod actuator.

Still further, it is an object of the present invention to provide an improvement for compression rod actuators which is simple in construction, efiicient in operation, and well-adapted for the purpose to which it is applicable.

SUMMARY OF THE INVENTION In accordance with the present invention, a compression rod actuator employing an elongated, hollow piston is provided with a slip-fit member freely disposed within the hollow piston which functions to add to the column strength without adding to the column load.

BRIEF DESCRIPTION OF THE DRAWING The novel features characteristic of the present invention, as well as additional objects and advantages thereof, will be understood better from the following detailed description when read in connection with the accompanying drawing. The drawing comprises a single figure which is a longitudinal section of a preferred embodiment of the present invention, the view being taken along the longitudinal axis thereof.

DESCRIPTION OF THE PREFERRED EMBODIMEN S Referring more particularly to the drawing, wherein similar reference characters have been used to designate corresponding parts throughout, the preferred embodiice ment of the present invention is shown applied to a conventional compression rod actuator 1.

The compression rod actuator comprises essentially a cooperating cylinder 3 and piston 5 arrangement for transmitting a force to suitable apparatus 7 to be energized. The piston is slidably disposed within the cylinder for reciprocation in response to fluid pressure imposed by oil or other suitable fluid 9 within the cylinder and supplied from a source (not shown). The function and operation of such actuators are well-known in the art.

The cylinder 3 is a hollow member which is disposed relatively stationary with respect to the reciprocating piston 5. The piston is an elongated, hOllOlW, cylindrical member having one end 11 closed which is attached in a suitable manner to apparatus 7 to be energized. The opposite end 13 of the piston is open for communication with the chamber 15 defined by the hollow cylinder and for receiving fluid 9 under pressure. A portion 19 of the outer surface 21 of the open end of the piston is of enlarged diameter and provided with an O-ring seal 23 for engagement with the inside surface 25 of the cylinder in a manner to effect a fluid tight seal and yet allow the piston to be freely slidable within the cylinder.

The combination of cylinder 3 and piston 5, Considered alone, is loaded in compression by the pressure acting on the diiferential between the piston external diameter and the internal diameter to get a specific magnitude of force transmitted at the piston closed end 11 for any given oil pressure. Thus, the piston diameter is a function of the force level and has a unique value for any particular force level; consequently, the parameters of the piston are functions of the other system parameters. If the length of this piston is such that it will fail as a solid column, it is advantageous to make it hollow since the inside portion contributes more to area than to moment of inertia. However the limitation imposed is that the wall thickness of the piston should be large enough to support the hoop stress caused by internal fluid pressure. In order to satisfy the condition where the wall thickness is not large enough to support the column load, in which case the piston is susceptible to buckling, the present invention proposes the use of a slip-fit member 27 disposed within the piston as an alternative to changing one or more of the system parameters.

The slip-fit member 27 comprises preferably a cylindrical member or tube, however, for some applications, a solid rod may be found suitable. In either case, the slipfit member is freely slidable within the piston and is disposed with its external surface in close proximity to the internal surface 29 of the piston. The length of the slip-fit member is less than that of the piston in order to allow freedom of movement axially. In other words, the slip-fit member, in eflFect, floats within the piston in the presence of a fluid medium. In order that the slip-fit member will not have a tendency to withdraw from the piston, a snap ring 31 is disposed adjacent to the open end 13 of the piston and within a groove 33 provided on the internal surface 29 of the piston.

In order to facilitate complete dispersion of the high pressure fiuid, the slip-fit tube may be provided with a plurality of openings 37 which extend through the wall thickness. Dispersion of the fluid is further facilitated by expanding the openings on the external surface of the slipfit member, in the manner illustrated in the drawing. This may be accomplished either by providing annular grooves 39 or annular raised surface areas 41 on the outer surface.

Disposing the slip-fit member in this manner within the piston effectively adds the value of its own moment of inertia to the stiffness of the piston without adding face area to the piston; consequently, the load on the piston is not changed. In other words, the slip-fit member lies completely within the high pressure environment, in a triaxial state of stress, without picking up any compression load, yet, effectively it will prevent column failure in the piston that is, buckling incident to loading in compression. Thus, it is not the intent of the slip-fit member 27 to reduce hoop stresses in the piston 5 caused by internal fluid pressure, but rather it is intended to provide an arrangement which will offer increased resistance to buckling of the assembly.

From the foregoing description, it will be recognized that the present invention provides a relatively simple arrangement for controlling stresses in a compression rod actuator. Although the invention has been described with respect to a single, preferred embodiment thereof, it will become obvious to persons skilled in the art that it is applicable to other situations and that changes and modifications are possible within the spirit of the present invention. Therefore, it is desired that the particular form of the present invention shown and described herein shall be considered as illustrative and not as limiting.

We claim:

1. A compression rod actuator comprising a housing, a hollow piston slidably received in said housing, said piston having one end thereof opening into the interior of said housing and having the opposite end thereof closed, means for applying a high pressure fluid from within said housing to the hollow interior of said piston, and supporting means freely disposed and contained within the hollow interior of said piston for controlling buckling of said piston.

2. The invention defined by claim 1 wherein said piston is disposed for reciprocation within said housing, said fluid means being responsive to drive said piston along said housing, and said supporting means comprises a hollow cylinder slidably disposed in proximity to the interior wall of said piston.

3. The invention as defined in claim 2 wherein said supporting means is provided with a plurality of openings extending through the wall thickness thereof to facilitate dispersion of said high pressure fluid.

4. The invention as defined in claim 3 wherein said openings are enlarged at the end thereof opening to the outer surface of said supporting means wall.

5. The invention as defined in claim 3 wherein the outer surface of said supporting means is provided with raised surface areas disposed between said openings in a manner to provide expanded openings in communication with said openings thereby to further facilitate dispersion of said high pressure fluid.

References Cited UNITED STATES PATENTS 2,147,031 2/1939 Hastings et a1. 13'826 2,475,105 7/1949 Mitton 9-2-113 X 2,646,504 7/1953 Gosline 9252 3,053,594 9/1962 Williamson 92165 3,270,626 9/1966 Bradbury 92-113 3,371,582 3/1968 Schmidt 92-52 FOREIGN PATENTS 1,066,632 1/1954 France.

MARTIN P. SCHWADRON, Primary Examiner. IRWIN C. COHEN, Assistant Examiner.

U.S. C1. X.R. 

